This invention relates to tensioners used with chain drives in automotive timing applications and more particularly to an integrated chain tensioner and tensioner arm.
Chain tensioning devices, such as hydraulic chain tensioners, are used as a control device for a power transmission chain, or any similar power transmission devices, as the chain travels between a plurality of sprockets. Generally, it is important to impart and maintain a certain degree of tension to the chain to prevent noises, slippage, or tooth jumping. Prevention of such tooth jumping is especially important in the case of a chain driven camshaft in an internal combustion engine because tooth jumping will throw off the camshaft timing by several degrees, possibly rendering the engine inoperative or causing damage. However, in the harsh environment in which an internal combustion engine operates, chain tension can vary between excessively high or low levels as a result of the wide variations in temperatures and differences between the coefficients of linear expansion among the various parts of the engine, including the chain and the tensioner. Moreover, wear to the chain components, during prolonged use, can result in a decrease in the tension of the chain. In addition, cam shaft and crank shaft induced torsional vibrations cause chain tension to vary considerably. This tension variation results in chain elongation, determined by chain stiffness.
Hydraulic chain tensioners typically have a plunger slidably fitted into a chamber and biased outward by a spring to provide tension to the chain. A lever, arm, or shoe is often used at the end of the plunger to assist in the tensioning of the chain. The hydraulic pressure from an external source, such as an oil pump or the like, flows into the chamber through passages formed in the housing. The plunger is easily moved outward by the combined efforts of the hydraulic pressure and the spring force.
When the plunger tends to move in a reverse direction (inward) away from the chain, typically a check valve is provided to restrict the flow of fluid from the chamber. In such a fashion, the tensioner achieves a so-called no-return function, i.e., movements are easy in one direction (outward) but difficult in the reverse direction (inward).
One example of a chain tensioner which uses a hydraulic tensioner and a pivoted lever to tension a chain is described in Sato et al., U.S. Pat. No. 5,318,482. Sato et al. show a conventional hydraulic tensioner with a plunger pressing a pivoted lever against a chain to impart an appropriate tension to the chain. The hydraulic tensioner and the pivoted lever, however, are completely separate from each other.
Another example of a chain tensioner which uses a hydraulic tensioner and a shoe to tension a chain is described in Suzuki et al., U.S. Pat. No. 5,314,388. Suzuki et al. show an oil-operated tensioner with a plunger forcing a shoe against a chain to impart a tension to the chain. The tensioner is continuously supplied with oil from an external source such as an oil pump. Furthermore, the shoe is mounted outside the tensioner on the outer end of the plunger.
Accordingly, it is an object of the present invention to provide a hydraulic chain tensioner that is an improvement over the prior art hydraulic chain tensioners. In the present invention, a hydraulic chain tensioner is integrated with a tensioner arm that has a fluid reservoir for supplying the hydraulic chain tensioner with oil. As a result, the integrated chain tensioner of the present invention is simpler and easier to install as compared to prior art hydraulic chain tensioners.